A water-soluble pyrazinium-based chemosensor for TNP detection: applications in MCF-7 cancer cell imaging and...

A pyrazinium-based Schiff base ligand, 3-((E)-(((Z)-2-amino-1,2-dicyanovinyl)imino)methyl)-1-benzylpyrazin-1-ium (BzPyz), was synthesized for the sensitive detection of TNP in aqueous media. The molecular structure of BzPyz was characterized using Fourier Transform Infrared Spectroscopy (FTIR), Powder X-ray Diffraction (PXRD), Nuclear Magnetic Resonance Spectroscopy (¹H and ¹³C NMR), and mass spectrometry. BzPyz exhibited blue emission in solution and yellowish-green fluorescence in the solid state, with pronounced solvatochromic behavior. Detailed photophysical studies indicated the involvement of both static and dynamic quenching pathways, with ground-state complex formation between BzPyz and TNP supporting a static contribution and (time-resolved photoluminescence) TRPL measurements providing evidence for an additional dynamic contribution arising from excited-state interactions. BzPyz exhibited a selective fluorescence turn-off response to TNP with a low detection limit of 4.43 nM. Spectroscopic analyses indicated a 1 : 1 binding stoichiometry for the [BzPyz-TNP] complex, with a strong binding affinity of K _a = 8.82 × 10⁴ M^-1. Density functional theory (DFT) calculations were performed to support the experimental findings by elucidating the ground-state electronic structure and transitions, with particular emphasis on interactions between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The practical applicability of BzPyz was demonstrated through successful quantification of TNP in real water and soil samples, validated by HPLC and spike recovery studies. This was extended to advanced in vitro cellular imaging in human breast adenocarcinoma (MCF-7) cells, latent fingerprint visualization, smartphone-assisted detection, molecular logic gate operation, and portable sensing platforms.